In the initial aftermath of the shooting, a spokesperson for the MPD said,

The suspect is a 23-year-old Milwaukee man with lengthy arrest record. The handgun he was armed with was taken in a burglary in Waukesha in March of this year.
The victim of that burglary reported 500 rounds of ammunition were also stolen with the handgun.
The officer is a 24-year-old, male, assigned to MPD's District 7. He has six years of service with MPD, three years as an officer. He was not injured and, as is standard practice, will be placed on administrative duty during the investigation and subsequent review by the Milwaukee County District Attorney's Office.